U.S. Pat. No. 3,670,299 to I. Kahn discloses a loudspeaker usable underwater, e.g. in swimming pools. The present invention concerns an improvement on the device shown in the Kahn patent, whereby the speaker can be used to relatively great water depths, e.g. sixty feet or more.
I am unaware of any prior art speaker designed to be used over a range of water depths, e.g. near the water surface and also at great water depths, e.g. greater than about ten feet. High water pressures associated with great water depths tend to bias the speaker membrane from its normal position, thereby displacing the voice coil from its properly centered position in the magnetic air gap.
It is possible to modify the speaker construction shown in above-referenced U.S. Pat. No. 3,670,299 for operation at large water depths. The modification involves the addition of pressurized air to the speaker housing such that the zone behind the speaker membrane is pressurized to reinforce the membrane against the biasing effect of water pressure on the outer face of the membrane.
However, when this is done then the speaker will not operate properly at other water pressures (higher or lower than the water pressure corresponding to the charging air pressure). I am proposing a pressure-equalizing system that is effective (useful) at any water pressure (within limits of the system), whereby the speaker can be operated over a range of water pressures.